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Introduction
Herbal products have recently been regulated in Canada in the class of natural health products (NHPs), which also includes vitamins, minerals and homeopathic remedies. Although generally regarded as safe by the public,1-3 there is growing evidence that herbal medicines can have clinically significant adverse effects and interactions with each other as well as with other medications.4-9 A formidable challenge for the field of herbal medicine pharmacovigilance is the under-reporting of suspected adverse drug reactions associated with herbal products.10,11
In North America, NHPs are commonly available for sale in pharmacies as well as at other retail outlets.12,13 The purpose of this paper is to describe a quick reference tool for identifying potential interactions between herbal and conventional pharmaceutical medications (see tool accompanying this issue of CPJ or go to www.cpjournal.ca); the tool was developed as part of a larger study, known as Pharmacy SONAR (Study Of Natural health product Adverse Reactions), investigating the feasibility of an active surveillance program for collecting NHP adverse event information in community pharmacies. This tool is not meant to replace access to high-quality databases or texts providing evidence-based information about natural health products including herbs - it is intended as a counselling aid to enhance the rapid identification of potentially harmful herbal medicine- drug combinations and to help the pharmacist identify when further information is needed to provide patient-specific advice.
Development of the Quick Reference Tool
The first step in creating the tool was the identification of the most commonly used herbal medicines in Canada. Extensive web-based and online database searches of MEDLINE and EMBASE were completed to identify Canadian population-based data.3 Given the scarcity of good population-based data, draft lists of "popular" herbal medicines were discussed by the Pharmacy SONAR steering committee (see acknowledgments for members) until consensus was reached regarding which herbal medicines should be included in the quick reference tool.
Second, conventional pharmaceutical medications common to community pharmacy settings were grouped into therapeutic categories and subgroups based on pharmacological properties. For example, the category "Gastrointestinal System" was divided into subgroups: laxative agents, antiulcer agents, antacid agents, antidiarrheal agents. Two additional categories were added based on the recommendations of our steering committee: herbal medicines with known (or suspected) nephrotoxicity or hepatotoxicity. The committee argued that even if...